Currently, lots of electronic equipment uses power supply devices based on a current transformer, which power supply devices at least include a current transformer and an energy storage capacitor. When the electronic equipment is switched on, the secondary winding of the current transformer in the power supply device outputs an electrical current to activate the energy storage capacitor and start to charge the same. Afterwards, the output voltage of the energy storage capacitor can supply power to a main circuit of the electronic equipment (other circuits except the power supply device, such as a signal processing circuit, etc.). For example, in the power distribution system, the electronic protection devices provided in switch devices such as Molded Case Circuit Breaker (MCCB) and Air Circuit Breaker (ACB), etc. are all equipped with the power supply device based on the current transformer. For example, the electronic protection device described here can be an Electronic Tripping Unit (ETU) or a Residual Current Device (RCD), etc.
However, because the current transformer of the power supply device only includes one two-lead secondary winding, when the electronic equipment is activated and enters the normal operating state, the current output by the secondary winding of the current transformer is substantially constant.
As such, the following problems will appear: if the number of turns of the secondary winding is set relatively large, then when the electronic equipment is activated, the current output by the secondary winding is so small that the activation time of the main circuit is relatively long. However, if the number of turns of the secondary winding is set relatively small so as to ensure a relatively short activation time of the main circuit, then when the electronic equipment is activated and enters the normal operating state, the electrical energy (i.e. output voltage) output by the energy storage capacitor in the power supply device still maintains a relatively high level, but at this moment, the electrical energy needed in the main circuit will decrease significantly, thereby wasting abundant electrical energy.